EP1552040B9 - Electrolytic cell leak limiter - Google Patents

Description

Field of the invention

The invention relates to the production of aluminum by igneous electrolysis. It relates more particularly to the means for confining gaseous effluents produced during electrolysis.

State of the art

Aluminum metal is produced industrially by igneous electrolysis, namely by electrolysis of alumina in solution in a bath of molten cryolite, called electrolyte bath, according to the well-known Hall-Héroult process. The electrolyte bath is contained in tanks, called "electrolysis cells", comprising a steel box, which is coated internally with refractory and / or insulating materials, and a cathode assembly located at the bottom of the tank. Anodes made of carbonaceous material are partially immersed in the electrolyte bath. The assembly formed by an electrolytic cell, its anodes and the electrolyte bath is called an electrolysis cell.

The electrolysis reaction, the secondary reactions and the high operating temperatures lead to the production of gaseous effluents, which mainly contain carbon dioxide and fluorinated products. The discharge of these effluents into the atmosphere is strictly controlled and regulated, not only with regard to the ambient atmosphere of the electrolysis room, for reasons of working conditions of the personnel operating near the cells, but also regarding air pollution. Several states' pollution regulations impose limits on the amount of effluent released to the atmosphere.

Today, there are solutions that can extract, recover and treat these effluents reliably and satisfactorily. A widely used solution consists in providing the electrolysis cells with an effluent collection device. This device covers the electrolysis tanks and comprises means of containment, which include in particular a rollover device, and means for suctioning and chemical treatment of the effluents. The known effluent treatment processes include the recovery of fluorinated gases by reaction with alumina. The cowling device comprises access means, such as covers, generally removable, and a casting door, which allow to intervene on the tank.

The rollover device delimits a confined suction zone and in depression with respect to the ambient atmosphere, which makes it possible to effectively recover the effluents. This results in steady-state capture efficiencies of over 97% in the most modern industrial facilities, so that the rates of atmospheric emissions of gaseous fluorinated products are well below regulatory thresholds.

In general, the anodes are connected to an electrical power supply bar, located outside the collection device, via metal rods which pass through the device through openings in the device. The free space (or "clearance") left by the rods in these openings is not sealed to allow vertical and horizontal movements of the metal rods. Vertical displacements are frequent and allow, in particular, to compensate for the wear of anodes during electrolysis. Horizontal displacements generally come from the replacement of spent anodes.

The free spaces between the anode rods and the inner edge of the passage openings constitute a rupture of confinement which is of small importance for each anode rod, but which becomes significant for all the anodes of a cell, and a fortiori for a series of several hundred cells.

Description of the invention

The present invention relates to a leak limiter adapted to reduce the confinement breakage from the passage openings of the anode rods. More specifically, the leakage limiter according to the invention is intended to limit the air and gas passages between the inside and the outside of the collection device of an aluminum production cell by igneous electrolysis through passage openings of the anode rods.

The leakage limiter of an electrolysis cell according to the invention is characterized in that it comprises at least one support, able to surround all or part of an anode rod, and at least one sealing body. flexible device arranged on all or part of the periphery and intended to close all or part of the free space between the inner edge of the passage openings and the anode rod.

The flexible body provides a certain seal around the anode rod and allows the maintenance of this seal, thanks to the flexibility of the body, despite inevitable variations in the position of the rod. In particular, the invention makes it possible to substantially limit gaseous exchanges by said free space.

The support is advantageously in the form of notch in order to simplify the construction of the leak limiter and to allow lateral insertion of an anode rod through the opening of the notch.

The subject of the invention is also an electrolysis cell comprising at least one leakage limiter according to the invention.

• La figure 1 représente, en coupe transversale, une cellule d'électrolyse typique destinée à la production d'aluminium.
• La figure 2 représente, en perspective et de manière simplifiée, une partie d'une cellule d'électrolyse typique destinée à la production d'aluminium, (a) sans et (b) avec un limiteur de fuite selon l'invention.
• Les figures 3 à 5 illustrent des limiteurs de fuite selon l'invention.
• La figure 6 illustre la brosse en U d'un limiteur de fuite selon une variante de l'invention.
• La figure 7 illustre une section transversale dans l'axe I de la brosse en U du limiteur de fuite illustré à la figure 5.
• La figure 8 illustre les sections de I' à C' du limiteur de fuite illustré à la figure 5.
• Les figures 9 et 10 illustrent des modes d'insertion d'une tige d'anode dans des limiteurs de fuite selon l'invention.

The invention will be better understood with the aid of the detailed description of a preferred embodiment thereof which is set forth below and which is illustrated with the aid of the appended figures.

• Figure 1 shows, in cross section, a typical electrolysis cell for the production of aluminum.
• Figure 2 shows, in perspective and in a simplified manner, a portion of a typical electrolysis cell for the production of aluminum, (a) without and (b) with a leakage limiter according to the invention.
• Figures 3 to 5 illustrate leakage limiters according to the invention.
• FIG. 6 illustrates the U-shaped brush of a leak limiter according to a variant of the invention.
• Figure 7 illustrates a cross-section in the I-axis of the U-brush of the leakage limiter illustrated in Figure 5.
• FIG. 8 illustrates the sections of I 'to C' of the leakage limiter illustrated in FIG. 5.
• FIGS. 9 and 10 illustrate modes of insertion of an anode rod into leakage limiters according to the invention.

As illustrated in FIG. 1, an electrolysis cell (1) for the production of aluminum by the Hall-Héroult method typically comprises a tank (10), anodes (2) supported by the fixing means typically comprising a rod (3) and a multipode (4) and mechanically and electrically connected to an anode frame (5) by means of connection means (6). The anode rod (3) is typically of substantially rectangular or square section. The tank (10) comprises a steel box (7), lining elements (8) and a cathode assembly (9). The coating elements (8) and the cathode assembly (9) form, inside the tank (10), a crucible adapted to contain the electrolyte bath (11) and a sheet of liquid metal (12) .

The electrolysis cell (1) also comprises a metal framework (13), which supports, in particular, the anode frame (5) in a mobile manner, and an effluent collection device comprising containment means (14, 15) and delimiting a confined interior space (16). The confinement means typically comprise removable hoods (14) and a fixed hood (15).

As shown in Figure 2 (a), the sensing device comprises openings (17) able to freely pass an anode rod (3). This opening usually takes the form of a slot to allow the insertion of an anode rod. The anodes (2) are generally introduced or removed from a lateral insertion electrolysis cell after removal of one or more covers (14). Therefore, the opening (17) is such that it allows a lateral insertion of the rod (3) of the anode (2), with or without longitudinal displacement thereof, that is to say with or without displacement thereof along the main axis of the cell.

Figure 2 (b) schematically illustrates the positioning of the leakage limiter (20) according to the invention in the passage opening of an anode (17).

The leakage limiter (20) of an electrolysis cell (1) for the production of aluminum provided with containment means (14, 15) having passage openings (17) for the insertion of anode rods (3), is characterized in that it comprises at least one support (21), able to surround all or part of an anode rod, and at least one flexible sealing body (30, 30a, 30b, 30c) disposed on all or part of the periphery (23) of the support (21) and intended to close all or part of the free space between the inner edge (18) of an opening (17) and an anode rod ( 3).

The support (21) can take various forms, such as substantially rectilinear, curved or other shapes. In addition, the support (21) may be formed of different elements.

In an advantageous embodiment of the invention, the one or more supports (21) form an opening, or "indentation", (26) capable of allowing lateral insertion. an anode rod (3). The opening (26) typically takes the form of a U or a three-sided frame. The sealing body or bodies (30, 30a, 30b, 30c) are disposed on the inner periphery (23) of the opening (26).

In this embodiment, the leakage limiter (20) surrounds at least three sides of the anode rod (3). The sealing body (30) can be of such shape that it also covers the fourth side of the rod. The leakage limiter (20) may optionally comprise a complementary closure element (20 '), movable or removable, adapted to limit leakage by the fourth side after insertion of the rod. This complementary closure element (20 ') may comprise a support (21') provided with a flexible sealing body (30 '). This complementary element may optionally be fixed to the fixed cover (15) or the movable cover (14) located near the anode rod.

Figure 3 illustrates the case where the seal body is formed of a single member (30). Figure 4 illustrates the case where the sealing body is formed of three separate elements (30a, 30b, 30c) juxtaposed.

As shown in Figure 5, the seal body abuts the anode rod, but is not necessarily in contact therewith. It can be separated by a few millimeters, typically 2 or 3 mm, without significantly reducing the sealing gain obtained with the device of the invention.

The flexible sealing body may be formed of any flexible element able to effectively seal all or part of said free space. It may, for example, be formed of son, lamellae, spongy body or flexible tubes, or any combination thereof. It can be metallic or non-metallic.

The flexible sealing body (30) is preferably adapted to withstand the atmosphere of the interior space (16) of the electrolysis cell and to maintain their mechanical properties at the temperatures reached in this environment.

The flexible sealing body (30) is advantageously formed of a bundle of metal and / or non-metallic wires. The Applicant has noted that the wire bundle allows the maintenance of a certain seal around the anode rod, thanks to the density of the wires, and that this seal is maintained, thanks to the flexibility of the wires, despite variations inevitable from the position of the rod. The wires also make it possible to maintain a good seal despite the surface defects of the anode rod.

It has been found very satisfying to use stainless steel wires. The sealing bodies formed of such son are resistant to mechanical stresses by the anode rod during its movements and have sufficient flexibility.

The wires of the bundle (30) are sufficiently tight to produce a significant pressure drop between the outside and the inside of the pickup device. It has been found sufficient to use a linear density of 100 to 1000 threads per centimeter along the periphery. The thickness of the beam is typically greater than 0.5 cm. The diameter of the wires is typically between 0.1 and 1 mm. The angle α of opening of the wire bundle is typically between 0 and 45 °, and more typically between 0 and 30 °. The length L of the metal wires leaving the support is typically between 1 and 10 cm.

According to an advantageous variant of the invention, at least one flexible sealing body (30, 30a, 30b, 30c) is fixed to a second support, or "mount", (32) movable relative to the support (21), that is to say able to move relative to the support (21).

In this variant, the support (21) typically has an elongate opening (22) on its inner periphery (23), and the mount (32) is movably inserted in this opening. The mount (32) and flexible sealing body (30, 30a, 30b, 30c) then form a moving assembly, or "drawer", (31) which improves the self-positioning of the sealing means during the movements of the anode rod. The movement of the mount / seal body assembly (31) is typically substantially perpendicular to the anode rod (3).

In this embodiment of the invention, the flexible sealing body (30, 30a, 30b, 30c) and the mount (32) are preferably of non-magnetic materials, so as not to develop magnetic force in the presence of the field intense magnetic reign in the environment of the cell, which avoids a blockage of movement by this magnetic field. For example, the mount (32) is preferably aluminum or aluminum alloy, and non-magnetic stainless steel son.

The mobility of the elements (31) in the support (21) can facilitate maintenance or replacement thereof in case of wear or damage.

Preferably, the leakage limiter (20) further comprises at least one connecting element (25) between the support (21) and the or each mount (32), for controlling the displacement of the sealing body or bodies (30). , 30a, 30b, 30c) relative to the support (21). The connecting element is typically attached to the mount (32). At least one connecting element is advantageously an elastic element, such as a spring or an elastic blade, in order to promote the self-positioning of the brush or brushes with respect to the anode rod (3). It may be possible to use rods and / or guide means, possibly combined with one or more elastic elements.

FIGS. 5 to 8 illustrate a preferred embodiment of the invention, in which the sealing body (30, 30a, 30b, 30c) is formed of wires fixed to a single movable frame (32) able to move by report to the framework (21).

FIG. 5 (b) corresponds to a longitudinal sectional view of the limiter of FIG. 5 (a) which reveals the mount / wire assembly (31), called a "brush", located partly inside the support (21). ). The profile of the anode rod (3) is seen in dotted lines. The Figure 6 shows the brush (31) alone, seen in its main plane (a) and view on the edge (b).

The lateral insertion of an anode rod (3) is normally along the axis II 'illustrated in FIGS. 5 and 6. FIGS. 9 and 10 illustrate two modes of insertion of an anode rod . Figure 9 corresponds to the case of a unidirectional insertion. Figure 10 corresponds to the case of bidirectional insertion with displacement of the leak limiter relative to the electrolysis cell.

The support (21) and the mount (32) are typically made of metal to ensure sufficient mechanical strength. Aluminum and aluminum alloys, which are non-magnetic, can advantageously be used.

The rigidity of the support (21) further allows the leak limiter to support, without deteriorating, the possible support of the foot of an operator.

The leakage limiter (20) can be fixed rigidly or movably to the electrolysis cell, and more specifically to a structural element thereof or to the sensing device. For this purpose, the support (21) advantageously comprises means (24) for securing it, preferably removably, to the electrolysis cell. A removable attachment, such as can be obtained for example by means of bolts and nuts (29), allows easy removal of the leak limiter without removing the anode.

Although a rigid fixation is sufficient in several cases, a movable attachment gives an additional degree of freedom to the leak limiter which allows an easier adaptation of its position relative to the anode rod. This additional degree of freedom is particularly useful when the passage opening (17) of the anode rod is of large size relative to the section of the rod and allows a large deflection thereof during its establishment. and / or its use.

This degree of freedom is also useful when the opening (17) has a more complicated shape than a simple slot and the engagement of the anode rod (3) in the opening (17) is bidirectional, it is that is to say that it comprises a displacement of the rod longitudinally and transversely to the main axis of the cell, such as that illustrated in FIG. 10. In such a case, the leakage limiter typically has an open position ( Figure 10 (a)) and a closed position (Figure 10 (b)). The leakage limiter (20) then advantageously comprises one or more complementary closure elements (33, 34), such as a plate, intended to maintain the tightness of the limiter during its movements. These complementary elements can be fixed or mobile. The leakage limiter (20) movable may optionally cooperate with one or more fixed shutter element (20 ') to maintain the tightness of the device during its movements. The movements of the leak limiter may be guided by a guide member (35), such as a rail.

When the leakage limiter (20) contains metallic elements, especially in the vicinity of the anode rod, such as a metal support or wires, it is preferable to electrically isolate the leakage limiter of the cell from the cell. electrolysis to avoid short circuits when handling the anode. This insulation can be obtained by interposing an electrical insulator (27, 28, 28 ') between the leakage limiter and the electrolysis cell. For example, in the case illustrated in FIG. 8, the leakage limiter (20) is isolated from the cell (1) by means of an insulating plate (27) interposed between the support (21) and the control means. containment (15) and using a tube (28) and a washer (28 ') interposed between the fastening means (29) and the confinement means (15).

The simplicity of the sealing mechanism of the leak limiter according to the invention gives it a satisfactory resistance to ambient conditions, and in particular the presence of alumina dust or ground bath which could block or stop mechanisms comprising axes. pivoting or rotating.

The leak limiter according to the invention also has the advantage of easily having a small volume. The total thickness of the limiter according to the invention is typically only 3 to 4 cm, which allows to easily position it between the anode frame (5) and the cover (15).

The invention also has the advantage of not requiring manual intervention or specific actuator, which simplifies its use and increases its reliability.

List of landmarks

1

Electrolysis cell

2

anodes

3

Fastening means and current supply (rod)

4

Means of fixing and current supply (multipode)

5

Anodic frame

6

Means for connecting the rod to the anode frame

7

box

8

Interior coating

9

Cathodic set

10

Tank

11

Electrolyte bath

12

Liquid aluminum

13

Metal frame

14

Means of containment (removable hood)

15

Means of containment (fixed hood)

16

Confined interior space

17

Opening passage of anode rod

18

Inner edge of the passage opening of anode rod

20

Leak limiter

20 '

Complementary shutter element

21, 21 '

Leakage limiter support

22

Extended opening

23

Inside rim of the support

24

Means of fixation

25

Connecting element

26

Opening of the limiter

27

Electrical insulation (plate)

28

Electrical insulation (tube)

28 '

Electrical insulation (washer)

29

Bolt and nut

30, 30a, 30b, 30c, 30 '

Flexible sealing body

31

Mobile mount / seal assembly

32

Mount

33, 34

Complementary shutter element

35

Guide means

Claims (14)

1. Leak limiter (20) of an electrolytic cell (1) for the production of aluminium provided with confinement means (14, 15) comprising passage openings (17) for the insertion of anode stems (3), characterized in that it comprises at least one support (21), capable of surrounding all or part of an anode stem, and at least one flexible sealing body (30, 30a, 30b, 30c) arranged around all or part of the periphery (23) of the support (21) and designed to close off all or some of the free space between the inside edge (18) of an opening (17) and an anode stem (3), and in that the support(s) (21) form an opening, or « notch » (26), through which an anode stem (3) can be inserted laterally.
2. Leak limiter (20) according to claim 1, characterised in that the flexible sealing body (30, 30a, 30b, 30c) is made of at least one element selected among wires, strips, spongy substances or flexible tubes, or any combination thereof.
3. Leak limiter (20) according to claim 1, characterised in that the or each flexible sealing body (30, 30a, 30b, 30c) is formed from a bundle of metallic and / or non-metallic wires.
4. Leak limiter (20) according to claim 3, characterised in that the bundle is composed of stainless steel wires.
5. Leak limiter (20) according to any one of claims 1 to 4, characterised in that at least one flexible sealing body (30, 30a, 30b, 30c) is fixed to a second support or « frame », (32) free to move with respect to the support (21).
6. Leak limiter (20) according to claim 5, characterised in that the said flexible sealing body (30, 30a, 30b, 30c) and the frame (32) are made of nonmagnetic materials.
7. Leak limiter (20) according to either of claims 5 or 6, characterised in that it also comprises at least one connecting element (25) between the support (21) and the or each frame (32), to control the displacement of the sealing body(ies) (30, 30a, 30b, 30c) with respect to the support (21).
8. Leak limiter (20) according to claim 7, characterised in that at least one connecting element (25) is an elastic element.
9. Electrolytic cell (1), characterised in that it comprises at least one leak limiter (20) according to any one of claims 1 to 8.
10. Electrolytic cell (1) according to claim 9, characterised in that the or each leak limiter (20) is rigidly fixed to the cell.
11. Electrolytic cell (1) according to claim 9, characterised in that the or each leak limiter (20) is fixed to the cell, free to move.
12. Electrolytic cell (1) according to claim 11, characterised in that the or each leak limiter (20) comprises at least one complementary closing element (33, 34) designed to maintain leak tightness of each limiter (20) during its displacements.
13. Electrolytic cell (1) as claimed in any of claims 9 to 12, characterised in that the or each leak limiter (20) is fixed to the cell so as to be removable.
14. Electrolytic cell (1) as claimed in any one of claims 9 to 13, characterised in that at least one electrical insulator (27, 28, 28') is inserted between the cell (1) and at least one leak limiter (20).

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